1. Field of the Invention
The present invention relates to a cutting apparatus for cutting a workpiece such as a semiconductor wafer, an optical device wafer, or the like.
2. Description of the Related Art
According to the present semiconductor device fabrication process, a plurality of areas are defined on the surface of a substantially disk-shaped semiconductor wafer by a grid-like pattern of division lines called streets, and devices of ICs, LSI circuits, or the like are formed in the defined areas. Then, the semiconductor wafer is cut along the streets to divide the areas into individual semiconductor chips. An optical device wafer including a layer of gallium nitride compound semiconductor or the like stacked on the surface of a sapphire substrate is also cut along streets into individual optical devices such as light-emitting diodes, laser diodes and CCDs for use in a wide range of electric appliances.
The wafer is cut along the streets by a cutting apparatus referred to as a dicer. The cutting apparatus includes a chuck table for supporting a workpiece such as a wafer, cutting means for cutting the workpiece held by the chuck table, and feeding means for feeding the chuck table and the cutting means relatively to each other. The cutting means includes a spindle unit having a rotating spindle, a cutting blade mounted on the rotating spindle, and a drive mechanism for rotating the rotating spindle. The cutting apparatus operates to feed the cutting blade and the workpiece held by the chuck table relatively to each other while the cutting blade is being rotated at a rotational speed ranging from 20,000 to 40,000 rpm.
The wafer with the devices formed thereon is made of hard brittle materials including silicon, sapphire, silicon nitride, glass and lithium tantalate. When the wafer is cut by the cutting blade, the cut surfaces may be chipped, lowering the quality of certain devices. Wafer materials such as sapphire with high Morse hardnesses are highly difficult, if not impossible, to cut with the cutting blade.
In order to solve the above problems, there has been proposed a cutting apparatus for applying an AC voltage to an ultrasonic transducer fixed to the surface of a cutting blade to ultrasonically vibrate the cutting blade while the cutting blade is cutting a workpiece (see, for example, Japanese Patent Laid-Open No. 2004-291636). However, the proposed cutting apparatus is disadvantageous in that it is difficult to transmit the ultrasonic vibrations generated by the ultrasonic transducer in a sufficient amplitude range.